1. Field of the Invention
The present invention relates to the well-known problem of ozone generation in electrostatic imaging machines, and provides a novel catalytic converter unit for receiving and uniformly neutralizing the ozoned air discharge from an electrostatic imaging machine, at a uniform high mass flow rate and with a minimum inlet pressure drop.
As is well known, ozone is generated in electrostatographic copying equipment as a result of corona discharge during sensitization of the recording surface of the photosensitive member. This is also true of other stations within the copier which employ corona discharge devices. Ozone emissions into the surrounding machine environment are controlled by catalytic xe2x80x9cfilteringxe2x80x9d devices capable of conversion of the ozone to relatively harmless substances and are located in the copier exhaust stream. These filters are generally characterized as fixed-bed devices; that is, the catalyst is impregnated into a porous support which is integrated within the copier exhaust housing or is incorporated into the corona discharge electrode structure itself. Each type of ozone control system described hereinabove is limited in its ability to neutralize the ozone due to the physical constraints placed upon the catalyst containing element.
As will be appreciated, the amount of exposure of the ozone laden vapors to the catalyst determines the capacity and efficiency of ozone neutralization by the catalyst-containing element. Where the catalyst is entrained within or coated upon a porous or fibrous support, ozone laden vapors must be capable of penetration of this structure at a uniform high flow rate for uniform exposure to the catalyst for an adequate dwell time.
2. Prior Art
U.S. Pat. No. 4,143,118 discloses an electrographic apparatus incorporating a catalyst-impregnated filter screen associated with a corotron and heater element to achieve in-situ ozone pre-neutralization prior to the transmission of the exhaust gas to an ozone-neutralization unit having a granular catalyst bed filter. Back-flushing is required to remove entrapped particles from blocking the outlet end of the unit and creating a substantial pressure drop which substantially reduces the flow rate and capacity of the unit.
U.S. Pat. No. 4,315,837 discloses an electrographic apparatus incorporating a composite support matrix, such as glass beads, coated with ozone-neutralizing catalyst to form a filter element within the exhaust conduit of the apparatus. The catalyst matrix is held in place, at each end, by a foraminous member which permits passage of the exhaust gas and retention of the composite catalyst matrix without appreciable pressure drop thereacross. The ozoned air must pass through the length of the catalyst bed and therefore the catalyst at the upstream or inlet end of the bed is exposed to most of the ozone and becomes depleted more quickly. Also the length of the catalyst bed presents a resistance to the ozoned air flow, resulting in an objectionable pressure drop, particularly in the case of more modern electrostatic copying machines which have ozone generation rates many times greater than conventional machines and which require a uniform high flow rate for the adequate neutralization of the larger volumes of ozone generated.
U.S. Pat. No. 4,388,274 discloses an electrographic copying machine incorporating an exhaust system for transporting the ozone-laden gas from each of the corona stations to an ozone-neutralizing catalyst unit containing a thin layer of ozone-decomposing catalyst retained between foraminous screens. The catalyst unit is not designed to expedite the flow rate of the ozoned air through the unit and therefore produces an objectionable inlet pressure drop which reduces the efficiency of the unit with respect to neutralizing large volumes of ozone, as produced by modern machines. Also, the catalyst bed is not designed to produce an optimum, even exposure and usage of the available catalyst volume. This results in a non-uniform depletion of the catalyst in some areas of the bed, and a non-uniform and incomplete neutralization of the ozone in the air discharged.
The present invention provides a novel, convenient catalytic converter unit for neutralizing an objectionable gas present in a gas present in a gas discharge, such as the ozoned air generated by electrographic copy machines at a uniform high flow rate, minimum inlet pressure drop, and optimum, even or uniform velocity through an catalyst bed capable of neutralizing the objectionable gas. These features are provided by the unique design of the present catalytic converted units. These include a cylindrical housing having a streamlined aerodynamic air inlet, which reduces inlet pressure drop and thereby increases air flow or throughput, whereby large volumes of ozone can be neutralized efficiently without necessitating a large capacity unit. The present design also includes a graduated-thickness cylindrical catalyst bed through which the ozoned air is directed for uniform exposure to the catalyst for adequate dwell time to produce uniform, complete neutralization of the ozone at high flow rate.